This is a study on the respiratory adjustments to inspiratory mechanical loading in humans and anesthetized cats. The responses and their mechanisms to both single breath and to continuous loading shall be examined. The objectives of the human studies are to examine the responses and the mechanisms of impairment in respiratory failure, in chronic obstructive lung disease, and to compare this data with pre-existent normal data or normal data obtained during this study. Examination will be made of the effects of chemical stimuli and the administration of oxygen on the progressive increase in inspiratory effort during continuous loading. The studies on the patients with respiratory failure shall also be used to develop simple methods of evaluating respiratory function as a guide to management and the need for controlled ventilation. The animal studies are complementary to the human studies and their aim is to demonstrate by neurophysiological techniques the role of chemical and non-chemical stimuli, their receptors, pathways, and the nature of the effector responses to single breath and to continuous loading. The data obtained in the human studies shall include the ventilatory and the inspiratory tracheal pressure responses to loading, lung volumes, and the mechanical properties of the respiratory system. By using on-line digital computer techniques the inspiratory muscle pressure responses, which are a direct estimate of the load adjustment mechanisms, shall be calculated. Similar respiratory data will be obtained in the cats, together with neurophysiological measurements of the activity of the phrenic nerve or the diaphragmatic EMG, and the external intercostal nerve or muscle EMG, and these shall be correlated with the inspiratory muscle pressure.